Mineral Colloids Continued

Na + K + K + Na + K + K + K + Cation Exchange Na +

Colloid Soil Solution

Factors Determining Cation Preference 1. Concentration 2. Charge (+1, +2,+3) 3. Size

Mineral Cation Exchange Capacity The total quantity of cations a clay can adsorb. Equal to the amount of charge Units are cmol c /kg soil Range: cmol c /kg Related directly to the amount of Isomorphous substitution

K HH O HH O HH O HH O +

1. Kaolinite 1. Has low CEC Reason: limited isomorphous substitution 2. Is non-expanding Reason: layers are “glued” shut by hydrogen bonds 3. Cation adsorption is on the outer mineral surfaces Reason: layers are “glued” shut by hydrogen bonds

2. Smectite 1. Has high CEC Reason: abundant isomorphous substitution (Mg for Al) 2. Is highly expanding 3. Cation adsorption is in the interlayers of mineral Reason: layers are not “glued” shut by hydrogen bonds Allowing easy movement of water and hydrated cations to the interlayer regions Reason: layers are not “glued” shut by hydrogen bonds Allowing easy movement of water and hydrated cations to the interlayer regions

3. Vermiculite 1. Has high CEC Reason: abundant isomorphous substitution (Al for Si) 2. Is moderately expanding 3. Cation adsorption is in the interlayers of mineral Reason: layers are not “glued” shut by hydrogen bonds Reason: layers are not “glued” shut by hydrogen bonds, but interlayer cations are very close to the source of the negative charge (the tetrahedra) holding the layers together.

3. Illite 1. Has low CEC Reason: abundant isomorphous substitution (Al for Si), but potassium ions fit well in cavities on the surface of the interlayers, holding them tightly together. 2. Is non-expanding 3. Cation adsorption is mostly on external mineral surfaces Reason: potassium ions fit well in cavities on the surface of the interlayers, holding them tightly together. Reason: potassium ions fit well in cavities on the surface of the interlayers, holding them tightly together. K K K Clay Layer

Minerals KaoliniteSmectiteVermiculite illite 1:1 None 2 – 5 2:1 High :1 Limited 100 – 160 2:1 None Mineral Expansion CEC (cmol/kg) Octahedral substitution tetrahedral substitution { tetrahedral substitution

Bt horizon E horizon A horizon B horizon (Illuvial) (Elluvial) Bt horizon t = accumulation of silicate clays formed in place or translocated from above Soils and Clays

Implications of Negative Charge sites. Important Cations: H +, Ca 2+, Mg 2+, Zn 2+, Mn 2+, K +, NH 4 +, Cu 2+ reserve Ca 2+ Mg 2+ Zn 2+ Cu 2+

Ca 2+ Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Root H+H+ H+H+ H+H+ H+H+

Flocculation and Dispersion

Na + Ca 2+ Particles with a Single Charge

Clay-Sized Particles Na Al 3+ DispersedFlocculated

High cation concentration Ambient concentration

Ambient solution cation concentration

Cations satisfying charge on both negatively charged colloids

Aids in development of soil structure Increases infiltration of water at the soil surface Can increase hydraulic conductivity Increases movement of gases (O 2 ) Aids in root penetration Flocculation

A Practical Matter for Flocculation

Wastewater Constituents Pathogenic organisms: bacteria, protozoa, viruses Non-pathogenic bacteria (> 100,000 / ml for sewage) Organic (carbon) particles: feces, food, plant material, humus Soluble Organics (carbon): pesticides, poisons, paints, drugs Soluble Inorganic Chemicals: nutrients (N and P), metals Inorganic particles: sand, silts, clays Organic and inorganic particles Higher turbidity levels are often associated with higher levels of viruses, parasites and bacteria. Turbidity

Primary Water Treatment

Primary Treatment Screening, Grit Removal, Primary Settling Bar Screen particles larger than ¼”

Grit Chamber Large particulates Short time period Sand and gravel esp. storm water V = KD 2

Primary Settling Tank Longer residence time Chemicals to promote flocculation/coagulation Smaller Particles Suspended solids Solids settle to the tank bottom as “primary sludge” Some remains as suspended solids

Al 3+ Chemical Flocculation Suspended silts, clays and organic matter are Generally small and negatively charged.

Primary Treatment Sludge Suspended solids

Iron and Aluminum Oxides/hydroxides

Weathering of Rocks and Minerals Rocks Primary Minerals Secondary Minerals chemical physical chemical Quartz Muscovite Feldspars biotite Silicate clays Fe oxides Al oxides Granite Basalt soluble constituents (Ca 2+, Mg 2+, K +, Fe 2+, Al 3+, Si 4+,CO 3 2 -, SO 4 2- )

Formation Increased Weathering Smectites Kaolinite Fe, Al oxides Hot, wet climates

Iron Oxides

Release of metal ions from minerals -SiO-Fe H + Fe OH-SI Iron bearing silicate Free iron Chemical weathering

Fe 2+ Fe 3+ oxygen Fe(OH) 3 water Lack of oxygen (Mobile)

Redoximorphic Features Fe 2+ Fe 3+

Iron Oxides Goethite Hematite ColorColor High soil temperature, better drained soils, rapid biomass turnover, high Fe-release rate from rocks most frequently occurring Fe-oxide in soil and has a characteristic yellowish brown color Bo Horizon Bo is an oxic subsurface horizon

Less weathered, poorer drainage More weathered, better drained Temperate Tropical Water and Temperature Goethite Hematite

Iron Oxides Can possess negative, positive, zero charge Potential interaction with cations and anions Cl -, F -, Br -, SO 4 2-, NO 3 -, CO 3 2-, PO 4 -3 Anion Exchange

Aluminum Oxides

Al 3+ Products of Extreme Weathering Breakdown of Al-O-Si linkages kaolinite Si, Al Removal by leaching water

Al 3+ Al(OH) 3 Water, crystallization Gibbsite (grayish-white color) The principal aluminum hydroxide in soil

Products of Extreme Weathering Al(OH) 3 Gibbsite crystalline and octahedral

Gibbsite Dominated Products of Extreme Weathering kaolinite Environments Highly weathered Less weathered Kaolinite Dominated Gibbsite Al(OH) 3

Aluminum Oxides Can possess negative, positive, zero charge Potential interaction with cations and anions Cl -, F -, Br -, SO 4 2-, NO 3 -, CO 3 2-, PO 4 -3 Anion Exchange Aluminum has a high affinity for phosphorus

Al 3+ Chemical Flocculation Suspended silts, clays and organic matter are Generally small and negatively charged.

Primary Treatment High in Al Suspended solids Aluminum has a high affinity for phosphorus

Both iron and aluminum oxides are prominent in highly weathered environments Can possess negative, positive, zero charge Both are capable of cation and anion exchange

Next: Organic Colloids